Comparative sectoriality in temperate hardwoods: hydraulics and xylem anatomy

Abstract

In wood, lateral transport of water and minerals occurs readily in 'integrated' trees but is more restricted in 'sectored species'. Dye distribution and a novel hydraulic technique are used to quantify species-specific differences in sectoriality in three temperate hardwoods, Betula papyrifera , Acer saccharum and Quercus rubra. Sectoriality was related to key elements of xylem structure: intervascular pitting, vessel diameter and vessel grouping. Perfusion of 0.5% safranin through isolated roots showed root-to-branch dye transport was most extensive in B. papyrifera and least extensive in Q. rubra . To test sectorialty using hydraulics, 20 m M KCl solution was pushed at 0.1 MPa through 5-cm wood segments, before and after occluding the direct axial outlet with glue, with flow rate measured in grams of solution expelled over time. Direct (axial) conductance (g MPa − 1 s − 1 ) through unglued outlets was compared with indirect (tangential) conductance around occluded outlets. Species with high indirect/direct conductance ratios (Integration Index) are the most integrated. Integration Index ranged from 0.26 in B. papyrifera to 0.02 in Q. rubra . Macerates showed that B. papyrifera has much greater percentage of cell wall area covered with intervascular pits than does A. saccharum or Q. rubra . Vessel grouping was closest in B. papyrifera and vessels were most isolated in Q. rubra . Widest diameter vessels occurred in Q. rubra , where they concentrated in springwood. Intervascular pitting, vessel diameter and grouping are wood traits that contribute to the continuum of sectoriality in trees, and may influence the ability of tree species to dominate in homogeneous or in patchy environments.

Analysis of Xylem Sap from Functional (Nonembolized) and Nonfunctional (Embolized) Vessels of Populus nigra: Chemistry of Refilling

“…Theoretical considerations suggesting that hydraulic isolation of xylem vessels is required for refilling (Vesala et al, 2003;Choat et al, 2009) may need to be further expanded to include temporal and spatial water potential disequilibria. Requirements for such hydraulic/ energy-isolated domains would underline the importance of stem transport sectoriality (Ellmore et al, 2006;Zanne et al, 2006), the persistence of leaf traces, and the role of phyllotaxy in protecting plants from embolism formation and allowing embolism repair against apparent energy gradients (Holbrook and Zwieniecki, 1999;Tyree et al, 1999;Zwieniecki and Holbrook, 2009). Temporal/spatial disequilibria of water potential in stems can also result from the hydraulic properties of xylem parenchyma cells if ratio of water volumes moving across them to resistance is relatively low.…”

Modeling the influence of differential sectoriality on the photosynthetic responses of understory saplings to patchy light and water availability

“…In this context, vascular sectoriality-the degree to which long distance resource transport is constrained to specific pathways between root and shoots-could pose an important limitation on photosynthetic potential and ultimately on growth (sensu Gloser et al 2008). Indeed, in a principal component analysis of 18 temperate woody species, Zanne et al (2006) noted a strong negative correlation between sectoriality and shade tolerance, which the authors hypothesized to reflect the benefits of low sectoriality under variable light conditions. We might also expect that under dry soil conditions, the ability to use the entire root system to supply water to high light leaves would extend the conditions in which leaves can effectively exploit light patches.…”

Ice Propagation in Dehardened Alpine Plant Species Studied by Infrared Differential Thermal Analysis (IDTA)

“…Leaf and branch junctions are known as potential water flow constrictions and segmentation points in the hydraulic architecture (Schulte and Brooks, 2003). The sectoriality of the vascular system describes the degree of hydraulic coupling between plant parts, which may range from full coupling to limited interconnectedness (Brooks et al, 2003;Schulte and Brooks, 2003;Orians et al, 2005;Ellmore et al, 2006;Zanne et al, 2006). Hydraulic sectoriality may explain the freezing pattern in S. acaulis with its highly branched shoot and S. incanus with leaves emerging from a compressed stem.…”